(1) Field of the Invention
The present invention relates to method for controlling a fuel injection amount of an internal combustion engine and an apparatus thereof for increasing a fuel injection amount in a high load state.
(2) Description of the Related Art
In general, in current internal combustion engines, the amount of fuel injected is increased in a high load state so that the air/fuel ratio is controlled to be rich (richer than the power air/fuel ratio at which the maximum power of the engine can be obtained), thereby supressing an increase in the temperature of the exhaust gas. Particularly, in turbo-charged engines, exhaust gas temperatures must be greatly decreased to improve engine durability. Accordingly, the fuel injection amount is usually greatly increased to obtain a rich air/fuel ratio.
However, when the fuel injection amount is increased in the high load state, the fuel consumption efficiency is degraded. In a prior art technique (Japanese Unexamined Patent Publication (Kokai) No. 58-51241) proposed to overcome this drawback, the engine running condition for increasing the fuel injection amount in the high load state is divided into a plurality of regions, and the fuel injection amount is increased for each region after a predetermined delay from the time at which the high load state is detected. This technique utilizes the fact that there is delay between the time when the exhaust temperature is increased and the time when the high load state is detected.
However, in the prior art technique for delaying the increase in the fuel injection amount, the following drawbacks are encountered:
(1) When the load becomes high and the combustion chamber temperature is increased, the engine is prone to knock. Therefore, where the fuel injection amount is not increased during the delay period, there is an undesirable effect on the durability of the engine.
(2) When the air/fuel ratio is too lean, since the exhaust gas temperature is quickly increased and the delay period for increasing the fuel injection amount becomes very short, the fuel consumption efficiency cannot be improved.
(3) During the delay period, since the air/fuel ratio is kept lean, a satisfactory output cannot be obtained, with a resulting poor acceleration response.